Physiology is the branch of biology that deals with the normal functions of living organisms and their parts.

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Physiology is the study of how the human body works. It describes the chemistry and physics behind basic body functions, from how molecules behave in cells to how systems of organs work together. It helps us understand what happens in a healthy body in everyday life and what goes wrong when someone gets sick.

Most of physiology depends on basic research studies carried out in a laboratory. Some physiologists study single proteins or cells, while others might do research on how cells interact to form tissues, organs, and systems within the body.

The cardiovascular system -- your heart and blood vessels

• The digestive system -- the stomach, intestines, and other organs that digest food

• The endocrine system -- glands that make hormones, the chemicals that control many body functions

• The immune system -- your body’s defense against germs and disease

• The muscular system -- the muscles you use to move your body

• The nervous system -- your brain, spinal cord, and nerves

• The renal system -- your kidneys and other organs that control the fluid in your body

• The reproductive system -- sex organs for men and women

• The respiratory system -- your lungs and airways

• The skeletal system -- bones, joints, cartilage, and connective tissue

For each system, physiology sheds light on the chemistry and physics of the structures involved. For example, physiologists have studied the electrical activity of cells in the heart that control its beat. They’re also exploring the process by which eyes detect light, from how the cells in the retina process light particles called photons to how the eyes send signals about images to the brain.

Physiology revolves around understanding how the human body maintains a steady state while adapting to outside conditions, a process called homeostasis. How do your organ systems keep your temperature relatively stable in different environments? How does your body keep your blood sugar and other chemical levels constant even when you eat different foods? These are the kinds of questions that physiologists aim to answer.

Physiology in Medicine

By shedding light on normal body functions, physiology can teach lessons about what goes wrong in disease. For instance, physiologists have figured out how different types of cells in the pancreas release hormones to control blood sugar levels. That helps doctors understand and treat diabetes.

The field also offers insights into how to make the human body work more efficiently. It’s often part of sports medicine, where knowing how the body adapts to physical challenges helps elite athletes improve their performance, avoid injury, and recover faster.